The present disclosure relates to semiconductor structures, and particularly to a replacement gate metal-oxide-semiconductor field effect transistor (MOSFET) having raised source/drain regions and methods of manufacturing the same.
As semiconductor devices shrink in each generation of semiconductor technology, the size of source and drain regions of a MOSFET decreases and the resistance of the source and drain regions increases correspondingly. While raised source/drain structures formed by selective epitaxy increase the thickness of source/drain regions and reduce source/drain resistance, a selective epitaxy process requires an elevated temperature, which tends to diffuse dopant atoms in source/drain extension regions that define the channel length of the MOSFET. Thus, the thermal cycling associated with selective epitaxy employed to form raised source/drain regions has a deleterious effect on performance of the MOSFET by variations in the channel length, which depend on the accuracy of temperature control during the epitaxy. However, precise control of the channel length is critical in providing uniform and reliable performance for a MOSFET.